1. Field of the Invention
The present invention relates generally to buoyant cable antennas and, more particularly, to a buoyant cable antenna with an antenna module for VLF/LF (Very Low Frequency/Low Frequency) bands and another antenna module for HF (High Frequency) band performance.
2. Description of the Prior Art
The buoyant cable antenna is one of a host of submarine antennas currently in use for communications. The buoyant cable antenna is utilized while the submarine is submerged. The legacy antenna in current use represents a compromise between VLF/LF performance and high frequency (HF) performance. The HF performance is, in fact, compromised by the need for a single antenna element to provide coverage at the HF and VLF/LF bands.
The following U.S. patents describe various prior art systems telemetry systems:
U.S. Pat. No. 4,476,576, issued Oct. 9, 1984, to Wheeler et al, discloses a VLF communication system which utilizes the electrically conducting portions of an electromechanical cable connected to a deployed aerostat which acts as its tether so as to additionally serve as the VLF antenna.
U.S. Pat. No. 4,760,348 and U.S. Pat. No. 4,774,519, issued Jul. 26, 1988 and Sep. 27, 1988, respectively, to Pease et. al., disclose a towable broadband submarine antenna system for deployment in the ocean operation, which comprises an antenna element including a metallic termination tip and a length of single conductor buoyant cable. A broadband amplifier connects to the antenna element and provides separate paths for the VLF/LF and the HF/VHF signals with amplification provided only to the HF/VHF signals. The signal from the broadband amplifier is further transmitted on a coaxial cable.
U.S. Pat. No. 5,252,984, issued Oct. 12, 1993, to Dorrie et al, discloses an elongated rod of dielectric material, for example fiberglass—plastic or the like, which has a central conductor located coaxially therein. The insulating rod is surrounded by a conductive layer, for example conductive lacquer, a mesh or braid of conductive material, a conductive foil or tube or the like. The bottom terminal of the central conductor will provide a high resistance output for the higher one of the frequency ranges which, for example, can be a radio telephone, or vehicular communication frequency of between 450-470 MHz. The entire antenna is suitable as an AM-FM/radio-telephone combination antenna. Preferably, the antenna is covered with a sleeve of insulating material, for example a heat shrinkable plastic. The band width of the antenna can be extended by placing a further electrically conductive layer on the rod, spaced by a gap (a) physically and electrically from the conductive layer in the middle of the elongated rod. The further conductive layer is connected to the inner coaxial conductor, which in turn can be coupled to an antenna input, for example the center conductor of a coaxial cable of a radio apparatus.
U.S. Pat. No. 5,606,329, issued Feb. 25, 1997, to Ramotowski et al, discloses a submarine buoyant cable antenna having positive buoyancy comprising a communications antenna electronics package encased in a polymer composition, the polymer composition comprising from about 80 percent to about 85 percent by weight of a room temperature curable thermosetting polymer having a viscosity, before curing, in the range of from about 700 to about 900 centipoise, and from about 15 percent to about 20 percent by weight of microballoons of a size ranging from about 20 to about 100 microns in diameter, the specific gravity of the composition being in the range of from about 0.51 to about 0.65 grams per cubic centimeter to provide the positive buoyancy.
U.S. Pat. No. 6,864,842, issued Mar. 8, 2005, to Hung et al, discloses a tri-band antenna that includes an insulative planar base, a low-frequency radiating portion, a high-frequency radiating portion, a first ground portion and a signal feeder cable. A resonating lacuna is defined between the first radiating portion and the first ground portion. The signal feeder cable includes an inner core wire and a metal braiding layer respectively soldered onto the connecting point of the low-frequency radiating portion and the high-frequency radiating portion and the first ground portion.
The above cited prior art does not disclose a modular buoyant cable antenna element suitable for submarine communications which provides the ability to optimize reception of signals in the very low frequency (VLF) and low frequency (LF) radio bands from 10 kHz-200 kHz as well as high frequency (HF) radio bands.